The present invention relates to a process for selectively and quantitatively converting nitrogen dioxide (NO.sub.2) in environmental atmosphere or exhaust from apparatus into nitrogen monoxide (NO) by reduction.
Nitrogen monoxide and nitrogen dioxide are main causative substances for forming photochemical smog, and hence the measurement of their concentrations in a precise manner is very important in a countermeasure for preventing air pollution.
For measurement of the above mentioned nitrogen oxides, an analyzer utilizing chemiluminescence is known (reference: Federal Register Vol. 36, No. 128, 1971). By the use of this analyzer, the concentration of nitrogen monoxide contained in environmental atmosphere or exhaust from apparatus can be measured precisely. For analysis of nitrogen dioxide, however, such analyzer necessitates the use of a converter capable of converting nitrogen dioxide into nitrogen monoxide. For such converter, carbon or a mixture of molybdenum oxide and carbon is used as reducing agent. However, a converter utilizing such reducing agent has such a drawback that it is effective only at high temperatures within a narrow range from 350.degree. C to 450.degree. C and such conditions apparently fail to make the conversion process efficient. Furthermore, there is an additional drawback that since the reducing agent used in this converter is influenced within such high temperature range by organonitrogen compounds such as peroxyacetly nitrate and alkyl nitrates, it is impossible in the presence of such compounds to selectively and quantitatively convert nitrogen dioxide alone into nitrogen monoxide.